Malaysian authorities have denied their efforts to find a missing passenger jet are mired in chaos, as they again doubled the search area to include areas hundreds of kilometres from the plane's flight path.

At a combative news conference on the fifth day of the vast hunt, transport minister Hishammuddin Hussein said officials would "never give up hope" of finding Malaysia Airlines flight MH370 and its 239 passengers and crew.

The hunt, involving 42 ships and 39 aircraft from several nations, had focused on Vietnam's South China Sea coast where the plane last made contact on Saturday.

The search has now been expanded to 43,500 square kilometres to include the Andaman Sea, west of Thailand, and the Malacca Strait, between the Malay Peninsula and the Indonesian island of Sumatra, both hundreds of kilometres away from where the plane vanished.

The change to the search area has fuelled allegations that the response is in disarray and lacking coordination.

Mr Hussein told the press conference a military radar had shown a plane heading west toward the Malacca Strait, but he could not say whether it was the missing Malaysia Airlines flight or confirm how low the plane was flying.

"That's why we are deploying all our best resources and also aircraft ... from near neighbouring countries in these two areas."

Officials have enraged passengers' relatives and sparked international ridicule for a series of contradictory and vague statements regarding the plane's fate.

"We are still doing search-and-rescue operations and we still have hope," civil aviation director Azharuddin Abdul Rahman said.

"Chances of survival depend also on a lot of criteria, because we don't know where the aircraft is."

Asked whether the search had now collapsed into confusion, Mr Hishammuddin said: "I don't think so. It's far from it. It's only confusion if you want it to be seen as confusion.

"I think it's not a matter of chaos. There are a lot of speculations that we have answered in the last few days."

Authorities investigate unidentified flying object

Air force chief Rodzali Daud said authorities were investigating an unidentified flying object about 320 kilometres north-west of the Malaysian state of Penang at 2:15am on Saturday.

That is hundreds of kilometres to the west of the plane's planned flight path between Kuala Lumpur and Beijing.

Authorities have said radar data records indicated the "possibility" that the plane may have attempted to "turn back" to Kuala Lumpur shortly before its disappearance, but have not revealed the specifics of the data.

"We are corroborating this. We are not saying this is MH370. It's an unidentified plot," General Rodzali said.

According to the data cited by General Rodzali, if the radar had spotted the missing plane, the aircraft would have flown for 45 minutes and dropped only about 1,500 metres in altitude since its sighting on civilian radar in the Gulf of Thailand.

There was no word on which direction it was then headed, but if this sighting was correct, the plane would have turned sharply west from its original course, travelling hundreds of kilometres over the Malay Peninsula from the Gulf of Thailand to the Andaman Sea.

This would put it in the northern part of the Strait of Malacca, roughly south of Phuket and east of the tip of Indonesia's Aceh province and India's Nicobar island chain.

Indonesia and Thailand have said their militaries detected no sign of any unusual aircraft in their airspace.

The US National Transportation Safety Board said in a statement that its experts in air traffic control and radar who travelled to Kuala Lumpur over the weekend were giving the Malaysians technical help in the search.

A US official in Washington said the experts were shown two sets of radar records, military and civilian, and they both appeared to show the plane turning to the west and across the Malay Peninsula.

But the official stressed the records were raw data returns that were not definitive.

Family of missing Australians hoping for a miracle

About two-thirds of the 227 passengers and 12 crew now presumed to have died aboard the plane were Chinese.